This invention relates to the electrical measurement art, and more particularly to a new and improved electrostatic voltmeter.
An electrostatic voltmeter is an instrument which measures electrostatic fields and electrostatic potentials on surfaces in a non-contacting manner, and such instruments include a probe or sensor assembly and an associated voltmeter circuit. This has been implemented by capacitive coupling between a detector surface in the probe and a surface bearing the field or potential being measured and by modulation of the capacitive coupling. The modulation has been performed by reciprocating the detector surface in a direction normal to the test surface, moving the detector surface into and out of registry with an aperture facing the test surface, or moving an interceding element to alternately expose and shield the detector surface with respect to the test surface.
Electrostatic voltmeters of this type are relatively expensive to manufacture because the mechanical arrangements needed for effecting capacitance modulation require relatively sophisticated manufacturing techniques and because the voltmeter systems must include a driver system for the mechanical modulator system and a demodulator for detecting the capacitively induced signals at the probe. Such mechanical arrangements with moving parts also present potential reliability problems. In addition, such electrostatic voltmeters of the modulated detector type are subject to a bandwidth limitation according to the Nyquist Sampling Theorm which limits the bandwidth of a sampling system to a maximum of one-half the sampling rate.